From: Neeraj Singh <neerajsi@xxxxxxxxxxxxx>
The new writeout-only mode attempts to tell the operating system to
flush its in-memory page cache to the storage hardware without issuing a
CACHE_FLUSH command to the storage controller.
Writeout-only fsync is significantly faster than a vanilla fsync on
common hardware, since data is written to a disk-side cache rather than
all the way to a durable medium. Later changes in this patch series will
take advantage of this primitive to implement batching of hardware
flushes.
When git_fsync is called with FSYNC_WRITEOUT_ONLY, it may fail and the
caller is expected to do an ordinary fsync as needed.
On Apple platforms, the fsync system call does not issue a CACHE_FLUSH
directive to the storage controller. This change updates fsync to do
fcntl(F_FULLFSYNC) to make fsync actually durable. We maintain parity
with existing behavior on Apple platforms by setting the default value
of the new core.fsyncmethod option.
Signed-off-by: Neeraj Singh <neerajsi@xxxxxxxxxxxxx>
---
Documentation/config/core.txt | 9 +++++
cache.h | 7 ++++
compat/mingw.h | 3 ++
compat/win32/flush.c | 28 +++++++++++++++
config.c | 12 +++++++
config.mak.uname | 3 ++
configure.ac | 8 +++++
contrib/buildsystems/CMakeLists.txt | 3 +-
environment.c | 2 +-
git-compat-util.h | 24 +++++++++++++
wrapper.c | 56 +++++++++++++++++++++++++++++
write-or-die.c | 10 +++---
12 files changed, 159 insertions(+), 6 deletions(-)
create mode 100644 compat/win32/flush.c
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index c04f62a54a1..c91eccea598 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -547,6 +547,15 @@ core.whitespace::
is relevant for `indent-with-non-tab` and when Git fixes `tab-in-indent`
errors. The default tab width is 8. Allowed values are 1 to 63.
+core.fsyncMethod::
+ A value indicating the strategy Git will use to harden repository data
+ using fsync and related primitives.
++
+* `fsync` uses the fsync() system call or platform equivalents.
+* `writeout-only` issues requests to send the writes to the storage
+ hardware, but does not send any FLUSH CACHE request. If the operating system
+ does not support the required interfaces, this falls back to fsync().
+
core.fsyncObjectFiles::
This boolean will enable 'fsync()' when writing object files.
+
diff --git a/cache.h b/cache.h
index eba12487b99..9cd60d94952 100644
--- a/cache.h
+++ b/cache.h
@@ -986,6 +986,13 @@ extern int read_replace_refs;
extern char *git_replace_ref_base;
extern int fsync_object_files;
+
+enum fsync_method {
+ FSYNC_METHOD_FSYNC,
+ FSYNC_METHOD_WRITEOUT_ONLY
+};
+
+extern enum fsync_method fsync_method;
extern int core_preload_index;
extern int precomposed_unicode;
extern int protect_hfs;
diff --git a/compat/mingw.h b/compat/mingw.h
index c9a52ad64a6..6074a3d3ced 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -329,6 +329,9 @@ int mingw_getpagesize(void);
#define getpagesize mingw_getpagesize
#endif
+int win32_fsync_no_flush(int fd);
+#define fsync_no_flush win32_fsync_no_flush
+
struct rlimit {
unsigned int rlim_cur;
};
diff --git a/compat/win32/flush.c b/compat/win32/flush.c
new file mode 100644
index 00000000000..75324c24ee7
--- /dev/null
+++ b/compat/win32/flush.c
@@ -0,0 +1,28 @@
+#include "../../git-compat-util.h"
+#include <winternl.h>
+#include "lazyload.h"
+
+int win32_fsync_no_flush(int fd)
+{
+ IO_STATUS_BLOCK io_status;
+
+#define FLUSH_FLAGS_FILE_DATA_ONLY 1
+
+ DECLARE_PROC_ADDR(ntdll.dll, NTSTATUS, NtFlushBuffersFileEx,
+ HANDLE FileHandle, ULONG Flags, PVOID Parameters, ULONG ParameterSize,
+ PIO_STATUS_BLOCK IoStatusBlock);
+
+ if (!INIT_PROC_ADDR(NtFlushBuffersFileEx)) {
+ errno = ENOSYS;
+ return -1;
+ }
+
+ memset(&io_status, 0, sizeof(io_status));
+ if (NtFlushBuffersFileEx((HANDLE)_get_osfhandle(fd), FLUSH_FLAGS_FILE_DATA_ONLY,
+ NULL, 0, &io_status)) {
+ errno = EINVAL;
+ return -1;
+ }
+
+ return 0;
+}
diff --git a/config.c b/config.c
index c5873f3a706..c3410b8a868 100644
--- a/config.c
+++ b/config.c
@@ -1490,6 +1490,18 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
return 0;
}
+ if (!strcmp(var, "core.fsyncmethod")) {
+ if (!value)
+ return config_error_nonbool(var);
+ if (!strcmp(value, "fsync"))
+ fsync_method = FSYNC_METHOD_FSYNC;
+ else if (!strcmp(value, "writeout-only"))
+ fsync_method = FSYNC_METHOD_WRITEOUT_ONLY;
+ else
+ warning(_("unknown %s value '%s'"), var, value);
+
+ }
+
if (!strcmp(var, "core.fsyncobjectfiles")) {
fsync_object_files = git_config_bool(var, value);
return 0;
diff --git a/config.mak.uname b/config.mak.uname
index d0701f9beb0..774a09622d2 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -57,6 +57,7 @@ ifeq ($(uname_S),Linux)
HAVE_CLOCK_MONOTONIC = YesPlease
# -lrt is needed for clock_gettime on glibc <= 2.16
NEEDS_LIBRT = YesPlease
+ HAVE_SYNC_FILE_RANGE = YesPlease
HAVE_GETDELIM = YesPlease
FREAD_READS_DIRECTORIES = UnfortunatelyYes
BASIC_CFLAGS += -DHAVE_SYSINFO
@@ -453,6 +454,7 @@ endif
CFLAGS =
BASIC_CFLAGS = -nologo -I. -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
COMPAT_OBJS = compat/msvc.o compat/winansi.o \
+ compat/win32/flush.o \
compat/win32/path-utils.o \
compat/win32/pthread.o compat/win32/syslog.o \
compat/win32/trace2_win32_process_info.o \
@@ -628,6 +630,7 @@ ifeq ($(uname_S),MINGW)
COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
COMPAT_OBJS += compat/mingw.o compat/winansi.o \
compat/win32/trace2_win32_process_info.o \
+ compat/win32/flush.o \
compat/win32/path-utils.o \
compat/win32/pthread.o compat/win32/syslog.o \
compat/win32/dirent.o
diff --git a/configure.ac b/configure.ac
index 5ee25ec95c8..6bd6bef1c44 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1082,6 +1082,14 @@ AC_COMPILE_IFELSE([CLOCK_MONOTONIC_SRC],
[AC_MSG_RESULT([no])
HAVE_CLOCK_MONOTONIC=])
GIT_CONF_SUBST([HAVE_CLOCK_MONOTONIC])
+
+#
+# Define HAVE_SYNC_FILE_RANGE=YesPlease if sync_file_range is available.
+GIT_CHECK_FUNC(sync_file_range,
+ [HAVE_SYNC_FILE_RANGE=YesPlease],
+ [HAVE_SYNC_FILE_RANGE])
+GIT_CONF_SUBST([HAVE_SYNC_FILE_RANGE])
+
#
# Define NO_SETITIMER if you don't have setitimer.
GIT_CHECK_FUNC(setitimer,
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 86b46114464..6d7bc16d054 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -261,7 +261,8 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
NOGDI OBJECT_CREATION_MODE=1 __USE_MINGW_ANSI_STDIO=0
USE_NED_ALLOCATOR OVERRIDE_STRDUP MMAP_PREVENTS_DELETE USE_WIN32_MMAP
UNICODE _UNICODE HAVE_WPGMPTR ENSURE_MSYSTEM_IS_SET)
- list(APPEND compat_SOURCES compat/mingw.c compat/winansi.c compat/win32/path-utils.c
+ list(APPEND compat_SOURCES compat/mingw.c compat/winansi.c
+ compat/win32/flush.c compat/win32/path-utils.c
compat/win32/pthread.c compat/win32mmap.c compat/win32/syslog.c
compat/win32/trace2_win32_process_info.c compat/win32/dirent.c
compat/nedmalloc/nedmalloc.c compat/strdup.c)
diff --git a/environment.c b/environment.c
index 9da7f3c1a19..f9140e842cf 100644
--- a/environment.c
+++ b/environment.c
@@ -41,7 +41,7 @@ const char *git_attributes_file;
const char *git_hooks_path;
int zlib_compression_level = Z_BEST_SPEED;
int pack_compression_level = Z_DEFAULT_COMPRESSION;
-int fsync_object_files;
+enum fsync_method fsync_method = FSYNC_METHOD_DEFAULT;
size_t packed_git_window_size = DEFAULT_PACKED_GIT_WINDOW_SIZE;
size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT;
size_t delta_base_cache_limit = 96 * 1024 * 1024;
diff --git a/git-compat-util.h b/git-compat-util.h
index c6bd2a84e55..cb9abd7a08c 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1239,6 +1239,30 @@ __attribute__((format (printf, 1, 2))) NORETURN
void BUG(const char *fmt, ...);
#endif
+#ifdef __APPLE__
+#define FSYNC_METHOD_DEFAULT FSYNC_METHOD_WRITEOUT_ONLY
+#else
+#define FSYNC_METHOD_DEFAULT FSYNC_METHOD_FSYNC
+#endif
+
+enum fsync_action {
+ FSYNC_WRITEOUT_ONLY,
+ FSYNC_HARDWARE_FLUSH
+};
+
+/*
+ * Issues an fsync against the specified file according to the specified mode.
+ *
+ * FSYNC_WRITEOUT_ONLY attempts to use interfaces available on some operating
+ * systems to flush the OS cache without issuing a flush command to the storage
+ * controller. If those interfaces are unavailable, the function fails with
+ * ENOSYS.
+ *
+ * FSYNC_HARDWARE_FLUSH does an OS writeout and hardware flush to ensure that
+ * changes are durable. It is not expected to fail.
+ */
+int git_fsync(int fd, enum fsync_action action);
+
/*
* Preserves errno, prints a message, but gives no warning for ENOENT.
* Returns 0 on success, which includes trying to unlink an object that does
diff --git a/wrapper.c b/wrapper.c
index 36e12119d76..1c5f2c87791 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -546,6 +546,62 @@ int xmkstemp_mode(char *filename_template, int mode)
return fd;
}
+int git_fsync(int fd, enum fsync_action action)
+{
+ switch (action) {
+ case FSYNC_WRITEOUT_ONLY:
+
+#ifdef __APPLE__
+ /*
+ * on macOS, fsync just causes filesystem cache writeback but does not
+ * flush hardware caches.
+ */
+ return fsync(fd);
+#endif
+
+#ifdef HAVE_SYNC_FILE_RANGE
+ /*
+ * On linux 2.6.17 and above, sync_file_range is the way to issue
+ * a writeback without a hardware flush. An offset of 0 and size of 0
+ * indicates writeout of the entire file and the wait flags ensure that all
+ * dirty data is written to the disk (potentially in a disk-side cache)
+ * before we continue.
+ */
+
+ return sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WAIT_BEFORE |
+ SYNC_FILE_RANGE_WRITE |
+ SYNC_FILE_RANGE_WAIT_AFTER);
+#endif
+
+#ifdef fsync_no_flush
+ return fsync_no_flush(fd);
+#endif
+
+ errno = ENOSYS;
+ return -1;
+
+ case FSYNC_HARDWARE_FLUSH:
+ /*
+ * On some platforms fsync may return EINTR. Try again in this
+ * case, since callers asking for a hardware flush may die if
+ * this function returns an error.
+ */
+ for (;;) {
+ int err;
+#ifdef __APPLE__
+ err = fcntl(fd, F_FULLFSYNC);
+#else
+ err = fsync(fd);
+#endif
+ if (err >= 0 || errno != EINTR)
+ return err;
+ }
+
+ default:
+ BUG("unexpected git_fsync(%d) call", action);
+ }
+}
+
static int warn_if_unremovable(const char *op, const char *file, int rc)
{
int err;
diff --git a/write-or-die.c b/write-or-die.c
index 0b1ec8190b6..0702acdd5e8 100644
--- a/write-or-die.c
+++ b/write-or-die.c
@@ -57,10 +57,12 @@ void fprintf_or_die(FILE *f, const char *fmt, ...)
void fsync_or_die(int fd, const char *msg)
{
- while (fsync(fd) < 0) {
- if (errno != EINTR)
- die_errno("fsync error on '%s'", msg);
- }
+ if (fsync_method == FSYNC_METHOD_WRITEOUT_ONLY &&
+ git_fsync(fd, FSYNC_WRITEOUT_ONLY) >= 0)
+ return;
+
+ if (git_fsync(fd, FSYNC_HARDWARE_FLUSH) < 0)
+ die_errno("fsync error on '%s'", msg);
}
void write_or_die(int fd, const void *buf, size_t count)
--
gitgitgadget
